This invention relates to fluid operated apparatus capable of providing a source of power or generating power and particularly relates to vertical axis wind mills or wind turbines.
The use of and capabilities of vertical axis wind turbines is known and these wind mills or wind turbines can take a variety of shapes and configurations. Fixed pitch, lift-type vertical axis wind turbines have until recently been limited in manufacture and use due to two main difficulties that have been encountered. Firstly, positive, aerodynamic overspeed control was not available for such turbines Also, the sizeable bending loads on the blades required the use of struts and/or wire to prevent bending. Alternatively, the blades must be shaped in a catenary form which reduces the bending loads on the blades to a minimum. The use of supporting struts and wires introduces drag and lowers the efficiency of the tubine while forming the blade in a catenary shape is difficult and expensive.
In U.S. Pat. No. 4,087,202 issued May 2, 1978 to National Research Development Corporation, there is taught a vertical axis wind turbine having two straight aerofoil-shaped blades, each of which is attached by a hinge to the outer end of a horizontally extending radial arm. The blades are each of aerofoil section NACA 0012 and have constant widths and thickness along their length. The arms are also of aerofoil section. A mechanism is provided which permits the blades to increase their angle of inclination relative to the vertical axis when the speed of rotation increases beyond the normal operating range whereby the rate of increase of rotational speed with wind speed is reduced.
U.S. Pat. No. 4,087,202 teaches a positive aerodynamic speed control mechanism that employs exposed tie wires and a spring. The exposed tie wires further reduce turbine efficiency under normal turbine speeds. Furthermore, it is believed that the Musgrove mechanism for limiting the speed of the wind turbine would not be very suitable for preventing turbine damage due to icing.